Three-dimensional numerical simulation of MHD waves observed by the Extreme Ultraviolet Imaging Telescope

We investigate the global large amplitude waves propagating across the sola r disk as observed by the SOHO/Extreme Ultraviolet Imaging Telescope (EIT). These waves appear to be similar to those observed in H-alpha in the chrom osphere and which are known as "Moreton waves," associated with large solar flares [Moreton, 1960, 1964]. Uchida [1968] interpreted these Moreton wave s as the propagation of a hydromagnetic disturbance in the corona with its wavefront intersecting the chromosphere to produce the Moreton wave as obse rved in movie sequences of H-alpha images. To search for an understanding o f the physical characteristics of these newly observed EIT waves, we constr ucted a three-dimensional, time-dependent, numerical magnetohydrodynamic (M HD) model. Measured global magnetic fields, obtained from the Wilcox Solar Observatory (WSO) at Stanford University, are used as the initial magnetic field to investigate hydromagnetic wave propagation in a three-dimensional spherical geometry. Using magnetohydrodynamic wave theory together with sim ulation, we are able to identify these observed EIT waves as fast mode MHD waves dominated by the acoustic mode, called magnetosonic waves. The result s to be presented include the following: (1) comparison of observed and sim ulated morphology projected on the disk and the distance-time curves on the solar disk; (2) three-dimensional evolution of the disturbed magnetic fiel d lines at various viewing angles; (3) evolution of the plasma density prof ile at a specific location as a function of latitude; and (4) computed Frie drich's diagrams to identify the MHD wave characteristics.